1. Field of the Invention
The invention relates to a cast wheel rim including a light-metal body which at least partially encompasses at least one shaped part forming a cast-in core and having a mean specific weight smaller than that of the light metal used for the casting.
2. Description of the Related Art
In order to reduce the dead weight of cast wheel rims, on the one hand, and to continue to safeguard a high strength of the wheel rim, on the other hand, attempts have been made for quite some time to provide in wheel rims hollow cores or lost cores having as low a specific dead weight as possible.
From DE 206 973 A, a wheel rim made of aluminum is known, in which various parts of the wheel are comprised of a hollow, resistant metal such as, e.g., steel or the like, forming hollow cores and being cast round by a light aluminum alloy.
It was likewise proposed (cf. e.g. DE 41 38 558 A) to produce wheel rims with hollow spokes which are produced by the aid of sand cores in the mold tool, said sand cores being removed from the rim after production.
Furthermore, a cast wheel rim is known from U.S. Pat. No. 3,253,862 A, which is produced by casting aluminum around a lost core comprised of metal wool.
WO 99/39923 A, moreover, describes a cast wheel rim in which a cast-in core is provided to reduce the dead weight of the cast wheel rim, said core having a lower specific weight than the light metal used for the casting and to this end being, in particular, a core part comprised of aluminum foam. The manufacture of such cast wheel rims involves problems, because the core cannot be preheated to the casting temperature and is heated as the light metal is being cast round, which causes gas present within said aluminum foam to expand, whereby strength-reducing gas inclusions are likely to occur in the light-metal wheel rim body. Preheating of the core part to the temperature of the liquid light metal—as would be desirable in order to avoid the expansion of enclosed air during the casting procedure—is not feasible since the aluminum-foam core part would loose its dimensional stability.